I rode my SR today as well. I did back to back rides on the two 650s, the SR and the 650SS.
The SR is very comfortable. The way the seat narrows at the front is ideal. The BSA frame narrows down here to match.
The Slimline Featherbed frame is 3 " narrower at this point than the old wide line Featherbed, but still much wider than the BSA. The Norton feels like you are sitting on top of the bike whereas with the BSA you feel more part of the bike.
Glen